This invention relates generally to ice cube making apparatus and more specifically to automatic apparatus for making ice cubes under various ambient temperature conditions.
For the purpose of making cube ice for commercial installations, such as restaurants, bars, motels and the like, there are a number of varieties of cube ice machines available on the market. Most of them include some type of chilled plate or mold in or against which water is delivered for freezing into ice cubes. The chilled member, which supplies the cooling for freezing the water, may be termed an evaporator plate, which conventionally includes refrigerant coils disposed on one side of the plate and on the reverse side some sort of pockets or recesses in which the water is frozen into cubes of ice. In some machines the evaporator plate is disposed horizontally and in some machines in a vertical position. Whichever disposition is utilized, the evaporator plate must be designed so that water may be delivered to the plate for freezing into cubes and the frozen cubes may thereafter be removed from the plate, or harvested, as such removal is termed.
In order to facilitate harvesting the ice, the evaporator plate in some machines is disposed in an angled position or a horizontal position with the ice forming molds facing downwardly so that the cubes may be harvested by gravity. That is an arrangement in which the cubes will fall out or away from the evaporator plate as soon as the bond between the two has been broken by thawing the ice at their interface. Examples of ice cube makers having gravity harvesting of the cubes are shown in the U.S. patents to Dedricks et al. No. 3,430,452, Johnson, No. 3,913,349, and Dwyer, No. 3,964,270. In the types of machines characterized by the Dedricks et al. patent and the Johnson patent, the evaporator plates are either in a vertical or near vertical position with the cube forming molds being provided by lattice configurations positioned on the evaporator plates on the side remote from the refrigerant coils. Water delivered across the top of the lattice structure runs downwardly across the face of the evaporator plate with portions thereof freezing in the pockets of the lattice as the water trickles across the plate. In the case of the Dedricks et al. patent structure, horizontally extending walls of the lattice are angled downwardly slightly so that the cubes may be harvested by gravity when released from the evaporator plate. Similarly, in the structure disclosed in the Johnson patent, the evaporator plates are tilted downwardly from the vertical so that the horizontal walls of the lattice are tilted downwardly, again, to permit gravity harvesting of the cubes. There are also similar commercial ice machines in which the evaporator plates are positioned vertically but which utilize mechanical harvesting means to disengage the cubes from a lattice work which is not inclined to permit the gravity harvest. One such machine is disclosed in the U.S. patent to Kattis, No. 3,144,755.
In most of these machines utilizing the lattice form of molds on generally vertically disposed evaporator plates, the ice making cycle is completed only when a complete slab is formed wherein the pockets in the lattice are full of ice and there are bridging connections between the adjacent rows of cubes to form a continuous slab in which all of the cubes are interconnected. The formation of a continuous slab is important since it facilitates the removal or harvesting of all of the cubes substantially simultaneously. If the cubes were not all connected in a single slab, minor variations in the temperature and the surface texture of the plate or the lattice would result in the cubes being harvested in a random manner with many of the cubes taking longer than average to be disengaged from the evaporator plate and the lattice unless the cubes are individually ejected as they are in some types of machines, as for instance is shown in the above cited Kattis patent. If there is not a mechanical ejector for each cube, the break-up of the slab and the random delivery of the cubes would necessitate lengthening the time for the harvesting portion of the cycle and would, therefore, cut down substantially on the output of the machine.
Accordingly, one of the main goals in ice machines of this general type is to form a proper slab of ice which is uniform across its face so that it may be harvested to produce maximum output from the machine. If the slab is not uniform in thickness, the bridging portions of ice will be weak in some areas having a tendency to break and thereby retard or prevent the rapid harvesting of all of the ice on the evaporator plate. It should also be noted that if the freezing cycle is extended sufficiently to build up sufficiently strong bridging portions in spite of the uneven freezing across the surface of the slab, the bridging portions in some areas will be very thick. It is well known that an ice machine is operating least efficiently during this terminal portion of the cycle when the water being frozen is insulated from the evaporator plate by a maximum thickness of ice. Therefore, it is important to the efficiency of the ice making machine that the cycle be terminated as soon as possible after the ice has built up over all of the conducting portions of the evaporator plate and its lattice structure.
The use of gravity for harvesting ice cubes in commercial ice making apparatus is advantageous since it permits the elimination of any mechanical or hydraulic means which might otherwise be used to displace the cubes from the lattice or molds in which they are formed. However, the force available from gravity to remove the cubes from their molds is very small and thereby introduces additional problems, which, in a large measure, offset the advantages obtainable by the use of gravity harvest. As an example of the kind of problem presented, it was noted above that there are often imperfections or nonuniformities in the evaporator plates which cause the cubes in one or more areas of the evaporator plate to be delayed in their discharge by gravity therefrom. In some instances, there may be a minor burr caused in the soldering, which burr might tend to restrain discharge of a cube from the mold until a substantial amount of thawing or melting of the cube has taken place. However, if a small amount of force is utilized in the harvesting operation of the cycle, any minor imperfections in the evaporator plate and its associated lattice structure would be largely overcome and the slab of ice could be harvested without an undue amount of melting.
Other factors which tend to increase the harvest time when relying on gravity harvest are such things as uneven thawing of the ice slab by the hot gases recycled through the evaporator coil. If the heat is not delivered evenly by the hot gases passing through the evaporator coil, there may tend to be substantial melting in some areas of the ice slab before there has been sufficient melting to completely release all of the cubes so that they will move by gravity out of the lattice structure. Also, the presence of the thin capillary film of water between the ice slab and the evaporator plate as the harvest cycle proceeds tends to create a significant force which is not easily overcome by the very light gravity forces acting on the slab of ice. Because of this retaining force produced by the capillary layer of water, it is often necessary to produce excessive melting before the capillary water drains and the ice slab is released to move by gravity out of the lattice structure.
In considering the refrigeration means associated with the evaporator plate in a typical ice machine, we have noted that the evaporator plate typically includes a coil secured to one side thereof through which the liquid refrigerant is passed. This coil typically takes the form of a copper tube which has a plurality of parallel horizontally disposed legs which traverse the rear face of the evaporator plate and are interconnected by radiused portions of tubing. A refrigerant supply line typically extends from the compressor through a condenser which may be either air or water cooled and then through an expansion valve to an input leg at the bottom of the evaporator plate. The liquid refrigerant than traverses the plate through the serpentine coil, passing back and forth through the adjacent horizontal legs in moving to the uppermost leg which is connected through to the input side of the compressor.
When the freezing cycle is completed and harvesting is begun, a solenoid valve in the refrigerant system is actuated, causing hot gas to be delivered to the evaporator coil instead of liquid refrigerant delivered during the freezing cycle. The hot gas quickly raises the temperature of the evaporator plate and the tubing as well as the lattice, causing the slab along with the cubes to be detached from the surfaces on which they were frozen. The harvesting may not take place immediately since there is a thin film of water between the ice and the evaporator plate including the lattice structure, which tends to retain the slab against the evaporator plate as a consequence of the capillary forces involved.
The lattice is provided with drain holes so that, as a slab moves slightly away from the evaporator plate, the water causing the capillary forces drains out from between the ice and the evaporator plate. Once the water has been drained, the slab may be harvested quickly and easily either by gravity or other means depending upon the type of machine involved.
As was indicated above, the gravity forces acting on a slab of ice are so small that excessive melting of the ice slab is often required before the capillary layer of water drains from between the ice and the evaporator plate. Although mechanical means have often been used in the past to separate or remove cube ice from the molds or lattice structure, such mechanical means have, in general, involved substantial forces which were intended to break the connection between the ice and the mold structure rather than being sufficient to overcome the capillary forces which retain the ice following the initial melting between the slab and the lattice structure.
The efficiency of an ice machine is easy to evaluate in terms of the pounds of ice produced in a 24-hour period by a compressor unit of some predetermined horsepower. It is conventional for manufacturers of ice machines to advertise and sell their ice machines on the basis of the pounds of ice which can be produced in a 24-hour period and the customers are used to buying the machines on this basis. However, it is well known that the actual capacity of an ice machine will vary considerably depending on the ambient conditions to which it is subjected in actual operation. Whether the machine utilizes an air-cooled condenser or a water-cooled condenser, the ambient air temperature or the temperature of the incoming water to the condenser will have a substantial effect on the heat which may be removed from the refrigerant during that portion of the cycle. Oftentimes, ice machines are located in the area of a motel swimming pool where ambient air and water might be above 90.degree. F. The same machine at another time of the year might be expected to function with air temperatures below freezing. Accordingly, it has been a continuing problem for the designers of ice machines to provide a control mechanism which would permit the machine to operate efficiently at varying ambient conditions.
Because of the cycle time variation attributable to the varying ambient conditions, it has been conventional to terminate the ice-making portion of the cycle by use of a sensor or probe which would engage an ice cube or ice slab to ascertain when the freezing process had been completed and the harvest portion of the cycle should begin. The use of such sensors or probes complicates the mechanism of the ice machine and provides an area which is very subject to malfunctioning problems. Accordingly, it would be preferable to employ control means for the freezing cycle which would not utilize probes and sensors which physically engage the ice being formed in the machine.
There are a number of examples in the prior art of ice machines having timers to control the ice making cycle. These examples include the U.S. Pats. to Roberts, No. 2,949,019 and Brysselbout, No. 3,254,501. The Brysselbout patent discloses a timer for controlling the freezing portion of the cycle with the time cycle initiated by a temperature-responsive switch associated with the evaporator plate. The Roberts patent, on the other hand, utilizes a pressure-responsive switch associated with the refrigerant line to initiate the timed harvest portion of the cycle.